The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) survey: A molecular gas line search
14 affiliations
- 1Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile
- 2Millennium Nucleus for Galaxies (MINGAL)
- 3Las Campanas Observatory, Carnegie Institution of Washington
- 4Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales
- 5Department of Astronomy, University of Washington
- 6Department of Physics, University of California
- 7Cosmic Dawn Center (DAWN)
- 8Blackett Lab, Imperial College London
- 9International Centre for Radio Astronomy Research (ICRAR), University of Western Australia
- 10Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM
- 11Space Telescope Science Institute
- 12Department of Physics & Astronomy, University of British Columbia
- 13Department of Physics and Astronomy, Texas A&M University
- 14Instituto de Alta Investigación, Universidad de Tarapacá
Abstract
Context. Current investigations of cold gas in the interstellar medium are limited by selection biases, as most samples are derived from optical or near-infrared surveys that preferentially select massive, low-obscuration galaxies. While previous research has established key scaling relations for the main sequence (MS), these studies often exclude gas-rich passive systems and inefficient star-forming populations that are not identified by conventional color-selection criteria. Overcoming these limitations requires a large-volume molecular-line survey that identifies galaxies based on their molecular gas reservoirs rather than stellar luminosity.
Aims. This study provides a census of molecular gas content in galaxies spanning a broad cosmic range (0.5 > z > 5) through a spectral search within the Extended Mapping of Obscuration to Reionization Survey (Ex-MORA) ALMA Band 4 observations.
Methods. The spectral axis of ALMA data in the Ex-MORA field, covering 577 arcmin ² , enabled a dual-strategy molecular line search: an unbiased search for high-significance line emitters and a targeted search utilizing spectroscopic redshift priors. In total, we detected 52 galaxies in CO or [C I ] line transitions, 2 of which exhibited two distinct lines. We derived physical properties using CIGALE with nonparametric star formation history modeling, and estimated molecular gas masses using metallicity-dependent conversion factors.
Results. Our sample is dominated by MS systems characterized by high stellar masses (median log M ⋆ /M ⊙ = 10.83) and substantial molecular gas reservoirs (>10 ¹⁰ M ⊙ ). The gas fraction ( μ gas ) increases with redshift among active populations; however, this trend may be influenced by environmental factors, particularly a significant bias at high redshifts due to a gas-rich protocluster at z ≈ 2.4. In contrast, the overdensity at z ≈ 0.73 is indistinguishable from the field population and does not bias the results. We identified five transitional green valley sources, all of which exhibit a peak in μ gas at cosmic noon. This peak could potentially be due to stellar feedback during this epoch that suppresses star formation by heating the gas rather than immediate reservoir depletion. Trying to conclude that this process happens to all green valley galaxies is beyond the scope and capabilities of our survey, but our results show that at least some GV galaxies could be affected by feedback. Our kinematic analysis of resolved sources indicates a predominance of rotating disk structures.
Conclusions. Large-area line searches are highly effective at recovering gas-massive galaxies across diverse evolutionary states, including transitional phases often missed by traditional surveys. The prevalence of MS systems and high gas masses underscores this approach’s ability to identify and characterize the most prominent gas reservoirs.
Related
- IRAC-Excess Galaxies in the NIRSpec Wide Survey: physical properties of bright EELGs at z∼7 and implications for Reionization
- The JWST Emission Line Survey (JELS): A narrow-band determination of the Hα Luminosity Function and Cosmic Star Formation into the Epoch of Reionization
- JWST lensed quasar dark matter survey. IV. Stringent warm dark matter constraints from the joint reconstruction of extended lensed arcs and quasar flux ratios
- GATOS XV: A JWST/MIRI survey of extended circumnuclear dust emission in nearby Seyfert galaxies
- The rise and decline of a transient obscuration event in a moderately distant type-I quasar
BibTeX
@article{catan2026extended,
title = {{The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) survey: A molecular gas line search}},
author = {V. Catán and J. González-López and M. Aravena and A. S. Long and C. M. Casey and D. L. Clements and E. da Cunha and M. Franco and A. M. Koekemoer and A. Man and J. Spilker and E. Treister},
journal = {Astronomy \& Astrophysics},
year = {2026},
month = oct,
doi = {10.1051/0004-6361/202661568},
url = {https://www.aanda.org/10.1051/0004-6361/202661568},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - The Extended Mapping Obscuration to Reionization with ALMA (Ex-MORA) survey: A molecular gas line search
AU - V. Catán
AU - J. González-López
AU - M. Aravena
AU - A. S. Long
AU - C. M. Casey
AU - D. L. Clements
AU - E. da Cunha
AU - M. Franco
AU - A. M. Koekemoer
AU - A. Man
AU - J. Spilker
AU - E. Treister
PY - 2026
DA - 2026/10/27
JO - Astronomy & Astrophysics
DO - 10.1051/0004-6361/202661568
UR - https://www.aanda.org/10.1051/0004-6361/202661568
AB - Context. Current investigations of cold gas in the interstellar medium are limited by selection biases, as most samples are derived from optical or near-infrared surveys that preferentially select massive, low-obscuration galaxies. While previous research has established key scaling relations for the main sequence (MS), these studies often exclude gas-rich passive systems and inefficient star-forming populations that are not identified by conventional color-selection criteria. Overcoming these limitations requires a large-volume molecular-line survey that identifies galaxies based on their molecular gas reservoirs rather than stellar luminosity. Aims. This study provides a census of molecular gas content in galaxies spanning a broad cosmic range (0.5 > z > 5) through a spectral search within the Extended Mapping of Obscuration to Reionization Survey (Ex-MORA) ALMA Band 4 observations. Methods. The spectral axis of ALMA data in the Ex-MORA field, covering 577 arcmin ² , enabled a dual-strategy molecular line search: an unbiased search for high-significance line emitters and a targeted search utilizing spectroscopic redshift priors. In total, we detected 52 galaxies in CO or [C I ] line transitions, 2 of which exhibited two distinct lines. We derived physical properties using CIGALE with nonparametric star formation history modeling, and estimated molecular gas masses using metallicity-dependent conversion factors. Results. Our sample is dominated by MS systems characterized by high stellar masses (median log M ⋆ /M ⊙ = 10.83) and substantial molecular gas reservoirs (>10 ¹⁰ M ⊙ ). The gas fraction ( μ gas ) increases with redshift among active populations; however, this trend may be influenced by environmental factors, particularly a significant bias at high redshifts due to a gas-rich protocluster at z ≈ 2.4. In contrast, the overdensity at z ≈ 0.73 is indistinguishable from the field population and does not bias the results. We identified five transitional green valley sources, all of which exhibit a peak in μ gas at cosmic noon. This peak could potentially be due to stellar feedback during this epoch that suppresses star formation by heating the gas rather than immediate reservoir depletion. Trying to conclude that this process happens to all green valley galaxies is beyond the scope and capabilities of our survey, but our results show that at least some GV galaxies could be affected by feedback. Our kinematic analysis of resolved sources indicates a predominance of rotating disk structures. Conclusions. Large-area line searches are highly effective at recovering gas-massive galaxies across diverse evolutionary states, including transitional phases often missed by traditional surveys. The prevalence of MS systems and high gas masses underscores this approach’s ability to identify and characterize the most prominent gas reservoirs.
SN - 0004-6361
SN - 1432-0746
ER -